The present invention relates generally to devices and methods for promoting blood circulation to the heart muscle. More particularly, the present invention relates to devices and methods for forming holes or channels in the interior walls of a heart chamber as part of a percutaneous myocardial revascularization (PMR) procedure.
Assuring that the heart muscle is adequately supplied with oxygen is critical to sustaining the life of a patient. To receive an adequate supply of oxygen, the heart muscle must be well perfused with blood. In a healthy heart, blood perfusion is accomplished with a system of blood vessels and capillaries. However, it is common for the blood vessels to become occluded (blocked) or stenotic (narrowed). A stenosis may be formed by an atheroma which is typically a hard, calcified substance which forms on the walls of a blood vessel.
Historically, individual stenotic lesions have been treated with a number of medical procedures including coronary bypass surgery, angioplasty, and atherectomy. Coronary bypass surgery typically involves utilizing vascular tissue from another part of the patient""s body to construct a shunt around the obstructed vessel. Angioplasty techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) are relatively non-invasive methods of treating a stenotic lesion. These angioplasty techniques typically involve the use of a guidewire and a balloon catheter. In these procedures, a balloon catheter is advanced over a guidewire such that the balloon is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened. A third technique which may be used to treat a stenotic lesion is atherectomy. During an atherectomy procedure, the stenotic lesion is mechanically cut or abraded away from the blood vessel wall.
Coronary by-pass, angioplasty, and atherectomy procedures have all been found effective in treating individual stenotic lesions in relatively large blood vessels. However, the heart muscle is perfused with blood through a network of small vessels and capillaries. In some cases, a large number of stenotic lesions may occur in a large number of locations throughout this network of small blood vessels and capillaries. The torturous path and small diameter of these blood vessels limit access to the stenotic lesions. The sheer number and small size of these stenotic lesions make techniques such as cardiovascular by-pass surgery, angioplasty, and atherectomy impractical.
When techniques that treat individual lesion are not practical, a technique known as percutaneous myocardial revascularization (PMR) may be used to improve the oxygenation of the myocardial tissue. A PMR procedure generally involves the creation of holes or channels directly into the myocardium of the heart. PMR was inspired in part by observations that reptilian heart muscles are supplied with oxygen primarily by blood perfusing directly from within heart chambers to the heart muscle. This contrasts with the human heart, which is supplied by coronary vessels receiving blood from the aorta. Positive clinical results have been demonstrated in human patients receiving PMR treatments. These results are believed to be caused because the myocardial tissue is oxygenated by blood flowing through the heart chamber into the newly created holes or channels. In addition, it is believed that new blood vessels may form when the holes and channels begin to heal, which is sometimes referred to as angiogenesis.
A number of methods have been used to create holes and/or channels in the myocardium during percutaneous myocardial revascularization. Methods of cutting include the use of knife-like cutting tools and cutting with light from a LASER. Radio frequency energy have also been used to burn or ablate channels or craters into the myocardial tissue.
A percutaneous myocardial revascularization (PMR) system in accordance with one embodiment of the present invention includes a first electrode disposed proximate the distal end of a catheter, a second electrode adapted for connection to the body of a patient, and a sensing block coupled to the first electrode and the second electrode. The sensing block is, preferably, adapted to receive electrical signals originating from the heart of the patient and provide an output signal that is related to the cardiac rhythm of the heart. The sensing block output signal may be displayed on a visual output display, and/or may be used to identify if the heart is in a particular wave or portion of the cardiac rhythm.
The PMR system also includes an ablation current source that is coupled to the first electrode and the second electrode for providing an ablation current that burns or ablates channels or craters in the myocardial tissue of the heart when activated. In a preferred embodiment, the ablation current source has an enabled state in which the ablation current passes between the first electrode and the second electrode, and a disabled state in which the ablation current is prevented from passing between the first electrode and the second electrode.
To control the ablation current source, an ablation controller may be provided. The ablation controller may provide an enable signal that controls whether the ablation current source is in the enabled state or the disabled state. The ablation controller preferably receives an output signal from the sensing block. The sensing block may sense a differential voltage between the first electrode and the second electrode, and provide an output signal that is related to the cardiac rhythm of the heart. The ablation controller may analyze the output signal from the sensing block and provide a detect signal when a selected triggering event occurs, such as when the voltage of the output signal crosses a preselected threshold voltage.
In a one embodiment, the detector of the ablation controller may provide a detect signal when the sensor block output signal indicates that the first electrode is touching the wall of the heart. The ablation controller may also provide a detect signal when the heart is in a less vulnerable portion of the cardiac rhythm, such as when the ventricles of the heart are contracting. As such, the ablation controller may be used to help identify when the first electrode is in contact with the wall of the heart, thereby reducing the likelihood that an ablation will be triggered when the first electrode is not in contact with the endocardium of the heart and cause damage to the blood platelets within the heart. The ablation controller may also be used to help synchronize ablation with less vulnerable portions or waves of the cardiac rhythm.